This invention is a development of a method of mooring a floating production and storage vessel (tanker) described in copending U.S. patent application Ser. No. 619,734. The present invention specifically relates to the method and apparatus for connecting the mooring riser to the floating vessel and allowing for relative motion between the two.
Patent application Ser. No. 619,734 discloses a method whereby the tanker is moored directly from the production riser that is deployable from the tanker. One advantage of this system is that it is very mobile and relatively insensitive to water depth. The complete floating system can therefore be deployed from one location to another quickly with negligible modifications and low cost.
Another feature of the mooring system is that it is not subjected to large wave loading. In most existing or proposed floating production mooring systems some form of buoyancy is incorporated in the system to provide a vertical force. This buoyancy is usually in the form of a buoy, with a buoyant tower or a buoyant yoke joining a tower to the tanker. The buoyant structure is of necessity large and in the wave zone which subjects it to very large forces. Although these forces are secondary in nature to the primary forces of mooring the tanker they are usually the dominant structural load. Patent application Ser. No. 619,734 uses a small diameter riser with no other mooring apparatus in the wave zone enabling a lighter structure to be used. For that particular invention an hydraulic motion compensation method was used. A further U.S. patent application filed June 12, 1984, Ser. No. 619,735 discloses a different method of motion compensation whereby a buoyancy can within the tanker provided the riser vertical reaction loads.